The present invention relates to a dental prosthetic device, and very specifically to a new form of dental crown, dental bridge, or like device. In relation to the disclosure herein of this invention, we use two specific terms regarding joinder--"cementing" and "bonding"--which terms are presented throughout the specification within quotation marks to indicate that they have specific meanings employed and understood conventionally in the dental art to describe two, generically different joinery mechanisms. The "cooperative" presence, usability and use of both of these mechanisms, according to the present invention, define advances in the art that are offered specifically by this invention. Also offered by the present invention are a prosthetic device and an installation practice which attend well to matters of aesthetics--i.e., final, in-place "appearance".
For the purpose of principal illustration herein, most of the discussion below is provided in relation to the structure and mounting of a dental crown. Reference to a dental crown is intended to include reference to a dental bridge, as well as to other like structures.
In the dental-crown-related prior art which is associated with this invention, there are fundamentally two different and relatively widely used predecessor crown structures and installation practices. Both have benefits and drawbacks. It is with regard to addressing and eliminating these drawbacks, while preserving and actually enhancing the benefits, that the present invention makes an important contribution to the dental art.
One prior art practice and structure involves preparing a crown which is formed with an aluminum oxide core (the part that seats, effectively, directly against a tooth preparation), and an overlying, outer porcelain jacket. Reference here to aluminum oxide, as well as later references herein to the same material, relate(s) to a conventionally available high-temperature ceramic material which includes aluminum oxide blended with one or more conventional sintering/binder material(s). This kind of crown, after it is built and properly shaped, is typically fitted onto a patient's tooth preparation and secured there by "cementing" it in place. This approach is fairly inexpensive in relation both to the cost of the crown unit per se, and to the specific installation procedure (the installation time required of a dentist). However, there is a recognized drawback which involves the durability of the joint interface that exists between such a crown and a tooth preparation, i.e., the interface between the tooth preparation and the aluminum oxide (or other) core. Apparently, it is very typical that the aluminum oxide core does not produce a good closure seal with a tooth surface, and this jeopardizes crown longevity in the mouth.
The other main prior art approach, one that is called an indirect approach, offers an installation that is considerably more robust in terms of longevity, but one that has the drawback that it is considerably more expensive in the context of installation. This approach involves the forming of a polyceramic crown directly onto a model of a tooth preparation without there being any intermediary aluminum oxide (or other) core. Once formed, the prepared crown is removed from the model for installation on the "natural" tooth preparation--i.e., directly into the mouth of the patient in a dentist's office. There, the polyceramic material in the crown is typically joined to the patient's tooth-preparation surface through a quite time-consuming technique referred to as "bonding" (as distinguished from "cementing"). This kind of crown and related installation, which works very well from a long-life sealing-to-a-tooth-preparation point of view, involves relatively high costs in relation to the typical, relatively long, dental-office "bonding" procedure, wherein a professional dentist's time (substantial time) is required.
It is to address the important issues of good bonding-longevity and overall low cost that the present invention focuses particular attention. As will become apparent, and as also was mentioned above, the invention additionally directs attention to the important matter of "in-place" aesthetics.
According to the invention, a multi-element dental prosthetic device is prepared (for example, a crown) which includes a high-temperature ceramic (preferably aluminum oxide) core, an outer polyceramic jacket, and a plural-layer intermediate layer structure which allows and promotes secure and economically achieved joinder effectively between the core and the jacket. This intermediate layer structure includes a porcelain layer next to the core, a layer of material known in the art as silane next to the porcelain layer, and a layer of a suitable conventional "bonding" material in between the silane layer and the outer jacket. While aluminum oxide is currently preferred as the core material, we recognize that many other kinds of high-temperature ceramic materials may be used. For example, one could employ a composite zirconium material to form the core.
The three-layer intermediate layer structure sets the stage, so-to-speak, and enables what can be considered to be the practical "bonding" of the polyceramic jacket to the ceramic core. This "bonding" condition, which is offered uniquely by the present invention, permits (a) the use of ceramic material as a core which can be joined by "cementing" to a tooth preparation, and (b) the use of polyceramic material in the jacket which most desirably "faces the outside world". In a manner of speaking, the mentioned silane intermediary layer plays a special role in permitting what is referred to herein as the effective joinder by "bonding" of the core and jacket. Silane acts as the linkage broker between the porcelain intermediary layer which anchors well to the ceramic core, and the "bonding"--material intermediary layer which anchors well to the polyceramic jacket. Absent the silane layer in this cooperative trio, the porcelain layer and the "bonding"--material layer would not affix to one another particularly well. Also, the "bonding"--material layer would not anchor well directly with the core material.
Our aluminum oxide core is formed in much the same manner as are currently used aluminum oxide cores, except that this new core is intentionally prepared to have certain outside dimensions that are determinedly reduced in relation to what they would most usually be in a conventional crown. In particular, our aluminum oxide core is appreciably smaller in height in relation to conventional aluminum oxide cores in order to expose an endless, somewhat annular, and generally channel-like region below the core for receiving an inwardly turned rim portion (or lower extremity portion) of the overlying, outer polyceramic jacket. In a final installation, this rim portion makes substantially direct contact with the stump and the associated shoulder in a tooth preparation, and this polyceramic-to-tooth (stump and shoulder) contact enables an especially good seal with a tooth preparation. Good "sealing", in turn, promotes long-life performance.
In the context of a dental crown device prepared in accordance with the present invention, the structural organization of this crown can be viewed, so-to-speak, from several different points of view.
From one point of view, the crown includes fundamentally two main components: (1) an inner, central, high-temperature, ceramic-material (preferably aluminum oxide) core that is directly joinable through "cementing" to the outside of the stump in a tooth preparation; and (2), an outer exposed jacket formed of a suitable polyceramic material, and joined, effectively, through "bonding" to the core.
From another point of view, the device built in accordance with this invention includes three principal components: (1) an inner, central, high-temperature, ceramic-material (preferably aluminum oxide) core that is directly joinable through "cementing" to the outside of the stump in a tooth preparation; (2) a thin, intermediary layer structure, including silane, which promotes "bonding" joinder between the core and a polyceramic jacket; and (3) an outer exposed jacket formed of a suitable polyceramic material joined by "bonding" to the core via the silane-containing, intermediary layer structure.
From yet another point of view, and without necessitating any specific reference to particular materials, the device of this invention includes: (1) a core element that is substantially directly joinable by "cementing" to the outside surface of the stump in a tooth preparation, with the lower extremity of this core element, when it is in place on a preparation stump, terminating short of the region where the stump and the shoulder in the tooth preparation join; and (2) an outer, jacketing wear material which is formed on (and joined effectively by "bonding" to) the outside of the core element, and which includes a lower extremity that, when in place on a tooth preparation, extends fully to the preparation shoulder just mentioned. This just-mentioned lower extremity of the jacketing material includes the inwardly turned rim portion discussed above, which rim portion extends inwardly toward the lower part of the outside surface of the tooth preparation stump, i.e., in a location beneath the lower extremity of the core element.